1. Field
The embodiments described herein relate generally to radiotherapy systems. More particularly, the described embodiments relate to providing an accurate independent measurement of a source trajectory for radiotherapy systems.
2. Description
Radiotherapy or radiation therapy is used to treat cancer and other diseases with ionizing radiation. A linear accelerator may be used to produce electrons or photons having particular energies. In one common application, a linear accelerator generates a radiation beam and directs the beam toward a target area of a patient. The beam is intended to injure or destroy cells within a target area by causing ionizations within the cells or other radiation-induced cell damage.
Radiation treatment plans are intended to maximize radiation delivered to a target while minimizing radiation delivered to healthy tissue. To design an effective radiation treatment plan, a designer must assume that the location and movement of the radiation source can be precisely known and controlled and that relevant portions of a patient will be in particular positions relative to the radiation source during delivery of the treatment radiation. The goals of maximizing target radiation and minimizing healthy tissue radiation may not be achieved if the location and movement of the radiation source are not positioned in accordance with the treatment plan during delivery of the radiation. More specifically, errors in positioning the radiation source can cause the delivery of low radiation doses to tumors and high radiation doses to sensitive healthy tissue. The potential for misdelivery increases with increased positioning and tracking (i.e., trajectory path) errors.
In a common embodiment of a radiotherapy system, a single radiation source is moved in a planar circular orbit about a target treatment area. The radiation is delivered in a cone from a fixed distance along a central axis at different positions along the circular orbit. Radiation delivered from the different positions ideally intersect or converge at a single point or cloud of points in space. That single point or cloud in space is referred to as the isocenter.
Conventional radiotherapy systems may be used to verify the position of the radiation source prior to delivery of treatment radiation to a patient. The verification is intended to confirm that the radiotherapy radiation is precisely delivered to relevant portions of a patient that will be positioned in accordance with a treatment plan. Some prior radiotherapy systems used film to detect the isocenter of the radiation. For example, the Winston-Lutz test may be used to verify the mechanical accuracy of the isocenter in radiotherapy.
However, the Winston-Lutz test and other procedures for determining and verifying the isocenter in radiotherapy have a number of limitations. Some procedures are limited to using radiograph film or other specific types of radiation detectors. As such, the accuracy of the isocenter determination is limited by the imaging resolution of the other specific types of radiation detectors and other physical limitations thereof (e.g., positioning, sensitivity, etc.) Some methods are limited to particular radiotherapy radiation source trajectories, either circular or non-circular. As such, the determination of the radioptherapy isocenter and thus the determination of the location of the radiation source is dependent on, for example, the radiotherapy radiation source trajectories of interest.
Systems are therefore desired for efficient determination of radiotherapy radiation source trajectory measurements.